The important part would seem to be the alignment of the needle on the shaft and it's calibration/accuracy afterwards. I hate to say this but I think you opened a can o' worms. You might need the assistance of a speedometer shop, if you can find one they should be able to help. If not try looking for an instrument repair shop (not musical
). Or you can keep pulling the needle on and off until it's close, determined by driving at a set speed, like 60mph = 2000rpm in fourth.....